When is the best time to add salt?

Ideally, you would want to taste and salt your dishes at each stage of the cooking process. Watch professional chefs on TV. If they make chili, for example, they brown the meat, they season and taste it. Then they add onions, garlic, tomatoes, they taste it, and season accordingly. After they have added the final ingredients and the cooking is completed, they taste and season it. Season at every stage.

(The only exception being if you have to add egg or milk based products at the end which might curdle, you should hold off salting at that stage until after the milk product has been incorporated, since excess salt could induce curdling.)